The present invention relates to the control of automatic or automated vehicle transmissions.
More precisely, it relates to a method for controlling an automatic transmission of a vehicle during cornering.
This invention has a favored but nonlimiting application for a motor vehicle with three or four wheels, equipped with a reducer or transmission with automated control, in which the linkage between the interface or gear selector handled by the driver and the control system of the transmission is of the “shift by wire” type. The movements imparted to the interface by the driver are then encoded electrically by the interface. The encoded signals travel through a wired or multiplexed network or another optical, telemetric, etc., communication medium to the control system of the transmission, where they are decoded and used by its calculation unit.
Some gear controls of automated reducers are not provided with means preventing selection of the neutral (dead point) position without positive unlocking action by the driver on a mechanical or electromechanical prevention system. This position may then be selected in error by the driver or by the control system itself. If this incident occurs in a straight line, or on a bend at low speed, there is no immediate impact on the road holding of the vehicle. If, on the other hand, this maneuver is carried out when negotiating a tight corner at high speed and with a high engine torque, the abrupt opening of the transmission may in the worst case result in leaving the road. This problem is exacerbated when the grip coefficient of the ground or the tire is lower. Its severity depends directly on the magnitude of the transverse acceleration of the vehicle during the incident.
When the system organizing the linkage between the driver and the control of the reducer is of the “shift by wire” i.e. electrical type, there is no mechanical linkage between the selector manipulated by the driver and the transmission itself. The data decoding the driver's intention regarding the control of the transmission are transcribed into signals to be sent to the control unit of the transmission. These data generally travel through a wired or multiplexed network, or alternatively an optical, telemetric, etc., medium. The position of the gear selector or stick available to the driver in his driving seat is sent to the control unit of the transmission and, after evaluation, allows the application of control logic of electrical or electrohydraulic actuators. This logic is normally related to the direction of the movement, or the parking of the vehicle, or the suitable gearbox ratio.
In the absence of prevention means, the neutral position may therefore be selected, in error or not, even though the kinematic chain is under torque. It may then impose opening of the transmission, that is to say of the kinematic chain thereof, under insufficiently safe conditions, particularly on a bend at high speed. Abrupt opening of the transmission then risks leading to a loss of control of the vehicle because of the centrifugal force, in particular when the grip coefficient of the ground or of the tires is low.